1. Field of the Invention
This invention relates to dampers for damping the opening motion of motor car dashboard doors or the doors of tape cassette cases built into video tape recorder (VTR) decks.
2. Description of the Prior Art
A motor car dashboard door or the door of a cassette case of a VTR deck has a hinge section spring-biased in the opening direction. When the dashboard door or case door is unlatched, it automatically opens under the influence of the biasing spring. However, if the opening operation relies upon the spring biasing force alone, sudden opening of the door and noise generation are liable to occur and, in the case of a cassette case, the cassette tape may be inadvertently ejected as a result of a shock to the case.
Accordingly, a damper is usually built into a hinge section of the dashboard door or case door in order to damp the biasing force of the spring and obtain a gentle and quiet opening operation.
The main purpose of the damper is to reduce the shock that would otherwise be experienced by means of the dashboard door or case door which is spring-biased in the opening direction when the dashboard door or case door is opened. When closing the dashboard door or case door, no damping action is needed since the dashboard door or case door is closed against the biasing force of the spring as well as its own weight, which may be controlled by the operator's hand. For this reason, the damper to be employed may be a one-way damper, that is, a damper having the function of damping rotation in only one direction.
There are different types of prior art one-way dampers. Among these dampers, the most typical one is that disclosed in Japanese Patent Public Disclosure No. SHO 61-24850. In this well-known one-way damper, as shown in FIG. 4, oil 2 is retained within a casing 1, and a braking plate 4 of a rotor 3 is immersed within the oil 2. A gear 6 is rotatably supported upon a shaft 5 of the rotor 3. A clutch spring 7 is provided upon the rotor shaft 5 and has an engagement portion 7a formed at one end, which is engaged within a slit 8 formed within the gear 6.
In use, when the gear 6 is rotated in a direction of storing a restoring force within the spring 7, the engagement portion 7a at one end of the spring 7 is also rotated so as to store a restoring force within the spring. This stored restoring force has the effect of restricting rotation of the rotor shaft 5 and offering a rotational resistance against the rotation of the gear 6. When the gear 6 is rotated in the opposite direction, the restoring force is released, thus causing slippage of the spring 7 upon the outer periphery of the rotor shaft 5 thereby releasing the resistance offered by means of the rotor 3.
This damper is a perfect one-way damper based upon the action of the clutch spring 7. However, it has the drawback that when the gear is coupled to the rotor, the torque of the gear is concentrated upon the engagement portion 7a of the spring 7, so that the engagement portion is liable to be elongated or broken. When the damper is installed as a means for damping the opening operation of a door, the door is liable to be forcibly opened by means of the operator's hand during the opening operation. In such a case, the engagement portion of the clutch spring is subject to damage, thereby destroying the damping function thereby.